"Mir, Ubuntu's in-progress replacement for the X Window System, is being used internally at Ubuntu developer Canonical and will be available to all users in the next version of the operating system. Mir was announced in March, with Canonical saying that a new display server is needed to power the Unity interface across desktops, phones, and tablets." Anyone here experience with Mir? Is it any good? any downsides?

In this case, barring something extremely unforeseen, it's going to cause isolation. Specifically Ubuntu's, and in all honesty that may just be Shuttleworth's endgame all along. Most of the rest of the Linux world has publicly aligned behind Wayland already.

The real fragmentation issues will come in between operating systems that run Wayland and those that don't or can't.